1. Field of the Invention
The invention pertains to the field of tensioners. More particularly, the invention pertains to a tensioner with a ratcheting device.
2. Description of the Related Art
Blade tensioners are commonly used to control a chain or belt where load fluctuations are not so severe as to over flex the spring or springs. A ratchet with backlash is added to tensioners to limit the effective backward or untensioned travel of a tensioning device.
Prior art FIG. 12 shows an example of a blade tensioner. The conventional blade tensioner 410 includes a blade shoe 411 made of resin having a curved chain sliding face and numerous blade springs 421, preferably made of metallic material. The blade springs 421 are arranged in layers on the opposite side of the blade shoe 411 from the chain sliding face, and provide spring force to the blade shoe 411. The ends of each spring-shaped blade spring 421 are inserted in the indented portions 414 and 415, which are formed in the distal portion 412 and proximal portion 413 of the blade shoe 411, respectively.
A bracket 417 is provided for mounting the blade tensioner 410 in an engine. Holes 418 and 419 are formed in the bracket 417, and mounting bolts are inserted into these holes 418 and 419. A sliding face 416 contacts the distal portion of the blade shoe 411 and permits sliding. The slide face 416 is formed on the distal portion of the bracket 417. A pin 420 supports the proximal portion 413 of the blade shoe 411 so that it may move in either direction. The pin 420 is secured on the bracket 417.
One example of a tensioner that uses a ratchet device is shown in prior art FIG. 9. The ratchet tensioner 301 comprises a tensioner housing 307 having a hole 312 for receiving a plunger 308 and a ratchet pawl 317 pivoted by a shaft 316 to the tensioner housing 307 and biased by a ratchet spring 318. The plunger 308 has teeth on one outer side that engage the ratchet pawl 317. The plunger 308 is biased out of the hole 312 to contact the tension lever 310 by fluid in the hollow section 313 and by the plunger spring 314. The tensioner lever 310 pivots on support shaft 309 and has a shoe surface 311 that contacts and applies tension to the slack side of the timing chain 306 wrapped around the camshaft 304 and its sprocket 305 and the crankshaft 302 and its sprocket 303. The plunger's 308 movement in and out of the hole 312 is limited by its teeth and the ratchet pawl 317 that engage them.
Prior art FIG. 10 shows a prior art blade tensioner with a bracket of U.S. Pat. No. 6,238,311, which is hereby incorporated by reference. A bracket 115 has a blade tensioner 100 attached on one side and on an opposite side from the blade tensioner a passive snubber 188 is attached to guide the chain (not shown). The blade tensioner 100 is comprised of a blade shoe 130 with a first end 142 and a second end 140. The first end 142 is attached to the bracket 115 by a pivot pin 190. A blade spring end is placed within the first end 142 and the second end 140 of the blade shoe 130 and pushes against the length of the blade shoe, causing it to bow slightly towards the chain. The second end 122 of the blade spring is secured to the blade shoe 130 by hollow roll pin 150. The blade spring causes the shoe to bow slightly. As the shoe heats up, the shoe bows even more until the chain prevents further bowing. Part of the bracket 115, adjacent to the second end of the shoe 140 is formed into a tab 135. The tab 135 is spaced outward from the bracket face and has a notch 145 aligned with the roll pin 150. The first end 142 of the blade shoe 130 pivots on pin 190. The blade shoe is kept on pin 190 by tab 135. When the retaining pin 155 is placed in the roll pin 150, the blade tensioner is held in a retracted position for shipping.
Prior art FIG. 11 shows a tensioner that uses a ratchet device. The tensioner includes a housing 270 having a bore 220 that receives a pair of pawls 250, 252 held in place by circlip 260. A piston 202, with grooves 211, is slidably received within bore 220 and is biased in a protruding direction from the bore 220 by spring 204. As the piston 202 moves in a protruding direction from the bore 220, the grooves 211 of the piston engage the teeth of pawls 250, 252.
The prior art does not show an adequate means of adding a ratchet device to a blade tensioner.